Conventionally, ball clutches and roller clutches have been provided as a safety device between a driving part and a driven part of a torque transmission mechanism so that the driving part may rotate idly when an overload is encountered in the driven part. Thus, possible damage to the transmission mechanism may be avoided.
In such an overload clutch, torque transmitting elements are held in hollow portions provided in one of a hub or a driven plate, and the torque transmitting elements are urged into recesses provided in the other of the hub or driven plate, thereby transmitting torque. When an overload is encountered in the driven part, the torque transmitting elements are adapted to escape from the recesses, thereby shutting off the torque transmission.
Conventionally, to enable the torque transmitting elements to move freely within the hollow portions during the escaping action, the elements are freely held within the hollow portions, namely by a substantial clearance.
However, with such a structure, when the driving part is reversely rotated, the clearance is liable to cause so-called "backlash", giving rise to relative displacement between the hub and the driven plate.
Moreover, even if the rotating direction is the same, the relative position between the hub and the driven plate may change due to the clearance after the overload condition has been removed.
It is possible to minimize the clearance by, for example, removing strain after heat treatment; however, such method entails a high manufacturing cost.
Accordingly, it is an object of this invention to provide an overload clutch in which the above-mentioned backlash may be eliminated and in which misalignment between the driving part and the driven plate may be absorbed. "Misalignment" refers to mounting error in terms of the spacing and the angular relative position between the driving part and the driven part.
Another object of this invention is to provide an overload clutch in which the backlash may be totally eliminated and in which torque transmission may be completely shut off in case of an overload being encountered.